I think you can get the information you need about work permits etc. from Ufficio Stranieri Milano. Every major town has its own Foreign(ers) Office I think. When I spoke with the Ufficio Stranieri in Treviso, I was told that the Italian Government is not issuing work permits to foreigners at the moment given the high levels of unemployment in the country. I don't know your chances with regards to setting up a business. You may need to find an immigration lawyer to help navigate the bureaucracy on that one.
If my experience in Treviso is anything to go by (ie: the same as other places in Italy) to obtain 'residence' you have to have an actual place of 'permanent' residence ie: an apartment (a B&B won't work). I got 'la residenza' when I finally was able to move into my apartment AND my rental agreement/lease was registered with the Agenzie del Entrate (Tax service) by the real estate agent. Once I had proof from the Agenzie del Entrate that my lease had been registered (officially stamped on the lease) THEN I was able to take that to the local Comune - Servizi Anagrafe - to get my address registered with them. Then I had to organize rubbish collection and transfer gas, water and electricity bills to my name. Most leases are for 3 or 5 years and you have to give six months notice if you want to quit the lease. And then there's the 'cauzione' - the bond you pay up-front - equivalent to three months rent in advance which you pay to the owner/landlord who holds it in trust after paying the real estate agent the equivalent of one months rent plus 22% (IVA) for his or her services.
To rent an apartment, all the real estate agents I consulted said I needed un reddito - an Italian tax return PLUS una busta paga - a monthly pay slip to provide proof of income sufficient to cover the rent PLUS a carta d'identita' (Italian identity card). If you don't have these, then you would need to find a guarantor who is willing to provide these documents and guarantee the rent if you bail out - ie. the guarantor is ultimately responsible for meeting the terms of the lease. That's a big ask for someone. Fortunately, I had a cousin who was willing to do that for me but my real estate agent spoke highly of me to the landlord (after submitting Una Proposta d'Affitto - Rental application) and in the end he didn't require those documents. He trusted me enough to pay the rent and all I needed for the lease was my passport and a codice fiscale (tax identification number which you get from the Agenzia del Entrate) plus a bank cheque for three months rent in advance (the 'cauzione') to give to the landlord who I met at the agent's office when we signed the paperwork. The agent effectively just provides a matchmaking service. After that you only deal with your landlord for everything.
The codice fiscale (which you also get from the Agenzia del Entrate) was the easiest thing to get because the government wants your taxes asap. You also need a codice fiscale to open a local bank account (to pay your rent by monthly bank transfer to your landlord's account using their IBAN #) and you also need a carta d'identita' to sign up with a local telephony company - IF you can also get a work permit (permesso di soggiorno per motivi di lavoro).
Italy is a real trip!
Good luck.